When wire line logging or perforating tools are introduced into wells that have surface pressure the tools are first placed inside a pipe system known as a lubricator which is attached to the well. The pressure tight lubricator tube is then pressured to the same pressure as the well, the well valve opened and the tool is then lowered into the well on the wire line to conduct its servicing operation. After the servicing operation has been completed, well servicing apparatus pulls upwardly on the wire line thus moving the servicing tool upwardly into the lubricator. After the well valve has been closed, well pressure is bled from the lubricator, after which the lubricator and tool are removed from the wellhead assembly.
During lubricator assembly and upon return of the tools from the well, the tools can be pulled against the internal stop of the lubricator system with sufficient force that the wire line cable can be accidently broken, thus releasing the tool. In the absence of a tool catching mechanism, the tool will fall to the lower portion of the well where it must then be retrieved by means of expensive and time consuming fishing operations. It is, of course, desirable to catch the tool string and to prevent it from falling downhole. Most cable heads are machined to provide a fishing neck that is intended for aiding recovery of tools lost downhole. The same fishing neck can be used to catch the cable head in the event the cable should become broken.